Non-toxic, non-corrosive, odorless gas generating composition

ABSTRACT

A nitrogen gas generating composition which upon combustion generates relatively low temperature non-toxic and odorless gases and low yield substantially non-corrosive and odorless solid decomposition products is achieved by using an alkali metal azide as the source of nitrogen gas and anhydrous chromic chloride as an oxidizer for the azide. In a preferred embodiment, the gas generating composition also contains aluminum oxide as an inert heat sink which cools the generated gases. The gas generating compositions of this invention are especially useful for inflating passgener vehicle protective crash bags.

States Patent 91 Lundstrom [4 1 Feb. 11, 1975 [75] Inventor: Norman H. Lundstrom, Brigham City, Utah [73] Assignee: Thiokol Chemical Corporation,

Bristol, Pa.

[22] Filed: Mar. 12, 1973 [2]] Appl. No.: 340,422

[56] References Cited UNITED STATES PATENTS 3/1973 Schaffer 280/150 AB 6/1973 Hendrickson et al........ 252/1883 R 12/1973 Price et a1. 280/150 AB 3,785,149 1/1974 Timmerman 280/150 AB 3,806,461 4/1974 Hendrickson et a1 188.3 R/ 3,814,694 6/1974 Klager et al 252/1883 R Primary Examiner-Benjamin R. Padgett Assistant Examiner-Irwin Gluck Attorney, Agent, or FirmThomas W. Brennan [57] ABSTRACT A nitrogen gas generating composition which upon combustion generates relatively low temperature nontoxic and odorless gases and low yield substantially non-corrosive and odorless solid decomposition products is achieved by using an alkali metal azide as the source of nitrogen gas and anhydrous chromic chloride as an oxidizer for the azide. In a preferred embodiment, the gas generating composition also contains aluminum oxide as an inert heat sink which cools the generated gases. The gas generating compositions of this invention are especially useful for inflating passgener vehicle protective crash bags.

11 Claims, No Drawings NON-TOXIC, NON-CORROSIVE, ODORLESS GAS GENERATING COMPOSITION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to non-toxic, substantially noncorrosive, odorless gas generating compositions. More particularly, this invention relates to nitrogen gas generating compositions for inflating passenger vehicle protective crash bags, which upon combustion generare relatively low temperature non-toxic odorless gases and substantially non-corrosive odorless solid decomposition products. While the present compositions are especially suited for the inflation of passenger protective crash bags in passenger vehicles, they are not lim ited to such an application since it is contemplated that these compositions may be employed in the inflation of other inflatable devices such as inflatable boats, rafts, escape ladders and the like.

2. Description of the Prior Art The concept of utilizing an inflatable bag orenvelope to protect passengers traveling in vehicles such as automobiles, boats, and aircraft during a collision or crash is generally known in the art. Such crash bags which are known in the art and which may be utilized in the practice of this invention are disclosed in U.S. Pat. Nos. 2,834,609; 3,117,424; 3,336,045; 3,450,414, and 3,573,885.

In the older devices, it was proposed that cylinders containing compressed gasbe used to inflate the crash bag. However, the use of compressed gas for this purpose revealed several very serious disadvantages. For example, it was found that the compressed gas devices were bulky and difficult to package compactly in places such as the steering column or dashboard of an automobile. Moreover, the compressed gas devices presented hazard in shipping, handling, and storage. The compressed gas inflation devices were also subject to the additional hazard of increased pressure in the con tainer as a result of high ambient temperatures. Finally, the compressed gas devices generally exhibited response times which are regarded as relatively slow.

Recently, it has been proposed to inflate these crash bags by utilizing gases generated from chemical gas generating compositions. However, such gas generating compositions must meet a number of requirements which have been difficult to entirely satisfy. The problem has been further complicated by the addition of even more restrictive requirements recently imposed by the automotive industry. These requirements including those recently imposed are as follows:

1. The gas generating composition must generate gases at a rate fast enough to inflate a crash bag within about 0.04 seconds.

2. The temperature of the gases produced by the gas generating composition must be relatively low in order to avoid burning the passenger in the event of bag rupture.

3. The gases produced by the gas generating composition must be non-toxic in order to prevent injury to the passenger by inhalation during bag rupture. This requirement has been strengthened to the point that even trace quantities of toxic gases should be eliminated.

4. The gas generating composition must be relatively insensitive to temperature changes.

5. The gas generating composition must be capable of being stored for long periods of time in the vehicle under conditions of vibration.

6. The gas generating composition must produce substantially non-corrosive solid decomposition products.

7. The gas generating composition must produce odor-free decomposition products.

Previous attempts to satisfy these requirements were directed toward the development of solid chemical gas generating compositions generally in the form of pellets or granules consisting of a gas containing source material and an oxidizer for the source material. For examples of these previously developed gas generating compositions see the pending applications of Price et al., Ser. No. 200,172 filed Nov. 18, 1972 now U.S. Pat. No. 3,779,823 Ser. No. 158,108 filed'June 29, 1971, now Pat. No. 3,741,585 incorporated herein by reference. Solid gas generating compositions of the above type are favored since they are better able to withstand the temperature variations and storage conditions encountered in passenger vehicle operations. The application of Hendrickson et al., referred to above discloses solid gas generating compositions consisting of a metallic or alkali metal azide as a nitrogen gas containing source material in combination with oxidizers therefor selected from metallic sulfides, metallic oxides, metallic iodides, organic iodides, organic chlorides, and sulfur. Price et al., disclose solid gas generating compositions containing a metallic or alkali metal azide in combination with oxidizers selected from metallic sulfides, metallic oxides, and sulfur, and in addition the use of a minor proportion of a polymeric binder to improve abrasion resistance. While the gas generating compositions of Hendrickson et a] and Price et al represented significant advances in the art of chemical gas generating compositions for passenger vehicle protective crash bags when they were developed, they have since been found to have several disadvantages in view of the present more restrictive requirements. In essence, the disadvantages of these prior art compositions are directly related to the nature and type of oxidizers employed therein. For example, the use of a metallic sulfide or sulfur as the oxidizer for an alkali metal azide such as NaN as taught by Hendrickson et al., or Price et al. during combustion produces Na s which is corrosive and readily hydrolyses to H S which is noxious and odorous. The use of a metallic oxide as the oxidizer for an alkali metal azide such as NaN in like manner produces an alkali metal oxide, i.e., Na O which is corrosive andreadily hydrolyses to NaOll-l. The use of metallic iodides as oxidizers as taught by Hendrickson et al., has surprisingly been found to yield on combustion free iodine gas which is toxic. For example, when chromium triiodide was evaluated as an oxidizer, it was discovered that minor proportions of iodine gas were produced during combustion. Thus, the use of metallic iodides as oxidizers does not meet the requirements relating to the complete elimination of toxic gases from the gas generating composition. The use of organic iodides and organic chlorides as oxidizers has been found to produce trace quantities of toxic gases during combustion because of the presence of the organic constituent. Finally, in using metallic iodides, organic iodides, and organic chloride as oxidizers, it has been found necessary to employ large quantities of these oxidizers because of their relatively slow reactivity thereby reducing the totalquantity of alkali metal azide which can be employed in the gas generating composition making the total composition less efficient. It is therefore evident that the previously proposed gas generating compositions fail to meetone or more of-the present requirements for compositions employed in inflating passenger 5 remaining after ignition prmcclive crash bags Alkali metal azides which may suitably be employed It is accordingly an object of the present invention to hl the COmPOShiOhSPf llh'eseht invention are a provide a gas generating composition capable of satisar 9 mlXhlres thereof- The 9 Preferred fying all of the various requirements outlined above. It alkah mfital compo-slhohs of the erating composition which generates non-toxic gases i having a relatively low temperature. It is still another Present Pomposmohs 1S anhydrous chrohhc l f h objgect of the present invention to provide a gas gener is egsentialcthat the anhydrokilis torm of this gxidizenbe ating composition which generates substantially nonid (i or er t e TL l arl corrosive and odorless solid decomposition products. It t;1 t iiz P t e g act is still further object of the present il'iVCl'ltlOF to provide :ty 2f r'nois t sfe lgg ng l i is; 211282 glyciun lSieaal'tliviviillllililea gas generating composition capable o producing gases at a sufficient rate to inflate a typical automobile m gf g i f l? g f fiz liazo wfhlch protective crash bag within about 0.04 seconds. Other s h l x3 2 objectsand advantages of the invention w ll be apparg gg c ig g ifi b 2:: 3 lj ent to those skilled in the art from the detailed descrip- 2 p f y y y p y g tion which follows. Own u In order to formulate the present gas generating com- SUMMARY OF THE INVENTION positions to asssure that substantially non-corrosive solid decom osition roducts roducts havin a H of It has been surprisingly and unexpectedly discovered from 4 to 9 Z herein)(apre formed ga that the objequveslsef forth above Caribe achlefed m bustion it is necessary that the quantities of alkali i g fg g r gi i i gigigg 3 :3 yg gl gz gz gf metal azide and anhydrous chromic chloride employed ride as the oxidiier a the azidey In a referred in the compositions be carefully controlled. Thus, it has p been found that in order to meet this objective the albgdlmemithe gas eneratmg c.omposmon also 00.nkali metal azide and anhydrous chromic chloride alummum oxlde as an heat Smk material should be used in quantities which are not in excess of whlch cools h gases generated It has been.found that a 10 percent variation in the stoichiometric ratio besuch compositions when formulated as described below tween these materials as shown in equations (1) and producedecomposition producits \(iivhicfh are non-toxic, 5 (2) above Accordingly the present Compositions substamallxnon'corhoswe an O i d should employ not more than from 2.8 to 3.2 moles of h sflbstantlany n9n'corroswe empgye alkali metal azide in combination with from 0.8 to L2 herein in relation to the solid decomposition pro ucts moles of anhydrous chromic chloride formed during combustion means that the solid decomwhile gas generating compositions containing alkali posmon products have a pH of from 4 to 40 metal azides and anhydrous chromic chloride as the DESCRIPTION-OF THE PREFERRED sole constituents are extremely useful and within the EMBODIMENTS scope ofthe present invention, the most preferred compositions of the present invention will additionally con- The dlrahle results prodhfied y the gas generating tain aluminum oxide as an inert heat sink material. The compositions of the Pre en i on are largely due aluminum oxide (A1 0 heat sink is inert in the sense to the inclusion in the mp s tions f an y rou hr that it takes no part in the reaction between the alkali mic chloride as the oxidizer for the alkali metal azides. tal azide and anhydrous chromic chloride but acts The advantages of using chromic chloride as the oxisolely as a coolant for the nitrogen gas generated durdizer can be seen by an examination of a typical stoiing combustion. The amount of aluminum oxide emchiometric reaction between an alkali metal azide such ployed in the preferred compositions may vary from as sodium azide and the chromic chloride. The reacabout 5 to about 15 percent, most preferably about 9 tions between these two components in an inert atmopercent, by weight of total gas generating composition. sphere and in air are shown in equations 1 and 2 which As will be apparent to those skilled in the art, it is necfollow. essary when incorporating aluminum oxide into the 2) Ignition 1) 3NaN CrCl A 4 1/2 N 3NaCl C1 (Air) Ignition 2) 3N21N CrCl a 4 1/2 N -l- 3NaCl C1 O As can be seen from the above reactions, the decomposition products formed are nitrogen, sodium chloride, and chromium metal or Cr O depending upon the atmosphere under which the reactions are carried for- 4 ward. These are decomposition products which are non-toxic, non-corrosive, and odorless. The fact that decomposition products are non-corrosive in nature can be readily determined by taking apH of the residue composition to adjust the quantities of alkali metal azide and chromic chloride in such a manner as to maintain the relative stoichiometry between them while accounting for the quantity of aluminum oxide sults have been obtained by the following procedure.

The alkali metal azide, e.g., NaN is first screened to obtain granules having a particle size of about -70 mesh. The oxidizer e.g., anhydrous chromic chloride is then ground utilizing a ball mill or fluid energy mill to an average particle diameter of from I to 3 microns. The 70 mesh particle size alkali metal azide, the ground chromic chloride, and if desired aluminum oxide and then blended together in a suitable blender, e.g., a paint shaker, V-blender, or dry powder blender. The blended product or mixture is then pressed into pellets by means of a suitable pressing apparatus, e.g., a Stokes press, to produce /2 inch pellets of gas generating composition. The pellets are then reduced to granular form and screened to recover a fraction having a particle size in the range of -6 to +10 mesh. As an alternative procedure, the /2 inch tablets of gas generating composition can be ground to produce a granular fraction having a particle size of mesh and then repressed to produce tablets having a diameter of /1 inch and a thickness of 0.05 inch. The A inch diameter tablets can then be employed in the gas generator in that form. This alternative procedure is advantageous in that the A tablets produced thereby exhibit better abrasion resistance than the finer particle size granules.

The following examples are submitted to further illustrate the nature of the present invention and are not intended as a limitation on the scope thereof.

EXAMPLES l and 2 In these examples, a gas generating composition of the present invention containing stoichiometric quantities of sodium azide and anhydrous chromic chloride was compared to a prior art gas generating composition containing stoichiometric quantities of sodium azide and molybdenum disulfide. The gas generating compositions were prepared in accordance with the procedure described above. In order to obtain combustion data on the gas generating compositions, samples of the compositions were tired into an evacuated metal gas collection chamber. A standard igniter composition such as a Boron-KNO igniter was employed in igniting the compositions. Formulations of the gas generating compositions are shown in percent by weight. Test results obtained upon combustion are shown below.

Measured in gas collection tank. All tests used 8.25 gram charge of propellant.

Measured at 200 miliseconds.

As the above data indicates, the gas generating com positions of the present invention, upon combustion yield non-toxic, substantially non-corrosive, and odor less decomposition products while a prior art gas generating composition on combustion produced corrosive decomposition products (as indicated by the pH of 10) and was odorous.

EXAMPLES 3 6 These examples illustrate the effect of aluminum oxide as a heat sink and coolant for the gas generating compositions of the present invention. In these examples, the formulation of Example 2 was employed as a control. In formulating the test compositions, aluminum oxide was added to the control formulation in quantities of 5 percent, 9 percent, and 15 percent by weight while the amounts of the sodium azide and chro' mic chloride components were adjusted proportionally to account for the addition in order to maintain a relative stoichiometric relationship between them. The various formulations were prepared in accordance with the procedure described previously and tested in the same manner as described in Examples 1 and 2. F ormulations and test results are shown below:

EXAMPLES 36 Percent by Weight Average of 2 to 3 tests on each composition.

EXAMPLE S 7 and 8 These examples illustrate the use of lithium azide in the compositions of the present invention. The compositions employed stoichiometric quantities of UN, and anhydrous CrCl and were prepared and tested in the manner described in Examples l6.

Percent by Weight Example Number 7 8 Formulation LiN 48.30 e 43.47 CrCl (Anhydrous) 51.70 46.53 Al203 I 10.00

Generator Test Data* Thermocouple Temperature (F).

at 200 Miliseconds 955 617 Action Time (Miliseconds) 23.9 22.5 Odor None None pH (Decomposition Residue) 6.6 5.6

Measured in gas collection tank. All tests used 825 gram charge of propellant.

The above data indicates that gas generating compositions containing MM; and anhydrous chromic chloride produces an efficient gas generating composition which upon combustion yields odorless and substantially non-corrosive decomposition products.

EXAMPLES 9 ll These examples illustrate the effect of varying the stoichiometry of the sodium azide-chromic chloride gas generating compositions. In these examples, the control composition based on stoichiometric quantities of NaN and CrCl was compared to a composition containing a 10 percent excess of CrCl and a composition containing 10 percent less CrCl (i.e., an excess of NaN than the theoretical stoichiometry between the materials. The compositions were prepared and tested in accordance with the procedure set forth in Examples l-8.

Percent by Weight The above data shows the effect of a 10 percent variation in the stoichiometric quantities of sodium azide and anhydrous chromic chloride. These compositions are considered to be acceptable for commercial use. However, a variation of more than 10 percent in the stoichiometric ratio of these ingredients is not recommended due to adverse effects on the pH of the decomposition products.

I claim:

1. A gas generating composition which upon combustion yields non-toxic, odorless gases, and substantially non-corrosive, and odorless solid decomposition products; said composition consisting essentially of:

a. from 2.8 to 3.2 moles of an alkali metal azide selected from the group consisting of sodium azide, lithium azide, and potassium azide; and

b. from 0.8 to 1.2 moles of anhydrous chromic chloride.

2. The composition as recited in claim 1 wherein the composition contains '3 moles of alkali'metal azide and 1 mole of anhydrous chromic chloride.

3. The composition as recited in claim 1 further containing from 5 to 15 percent by weight of aluminum oxide.

4. The composition as recited in claim 3 containing about 9 percent by weight of aluminum oxide.

5. The composition as recited in claim 1 wherein the alkali metal azide is sodium azide.

6. The composition as recited in claim 1 wherein the alkali metal azide is lithium azide.

7. The composition as recited in claim 1 wherein the alkali metal azide is potassium azide.

8. A gas generating composition which generates non-toxic, non-corrosive, odorless decomposition products consisting essentially of a. 50.16 percent NaN b. 40.75 percent Anhydrous CrCl and c. 9.09 percent M 0 9. A gas generating composition which generates non-toxic, non-corrosive, odorless decomposition products consisting essentially of a. 43.47 percent LiN b. 46.53 percent Anhydrous CrCl and c. 10 percent Al O 10. The method of making a gas generating composition containing an alkali metal azide, anhydrous chromic chloride, and aluminum oxide which comprises the steps of:

a. screening the alkali metal azide to obtain granules having a particle size of about mesh;

b. grinding an anhydrous chromic chloride to an average particle diameter of from 1 to 3 microns;

c. blending an alkali metal azide, chromic chloride,

and aluminum oxide to produce an intimate mixture of solids;

d. pressing the intimate solids mixture to produce pellets of gas generating composition;

e. grinding the pellets to produce granules of gas generating composition; and

f. screening the granules of gas generating composition to recover a fraction having a particle size of from 6 to +10 mesh.

11. The method as recited in claim 10 wherein the granules having a particle size of 20 mesh are repressed into pellets having a diameter of about A inch and a thickness of 0.05 inch. 

1. A GAS GENERATING COMPOSITION WHICH UPON COMBUSTION YIELDS NON-TOXIC, ODORLESS GASES, AND SUBSTANTIALLY NONCORROSIVE, AND ODORLESS SOLID DECOMPOSITION PRODUCTS, SAID COMPOSITION CONSISTING ESSENTIALLY OF: A. FROM 2.8 TO 3.2 MOLES OF AN ALKALI METAL AZIDE SELECTED FROM THE GROUP CONSISTING OF SODIUM AZIDE, LITHIUM AZIDE, AND POTASSIUM AZIDE, AND B. FROM 0.8 TO 1.2 MOLES OF ANHYDROUS CHROMIC CHLORIDE.
 2. The composition as recited in claim 1 wherein the composition contains 3 moles of alkali metal azide and 1 mole of anhydrous chromic chloride.
 3. The composition as recited in claim 1 further containing from 5 to 15 percent by weight of aluminum oxide.
 4. The composition as recited in claim 3 containing about 9 percent by weight of aluminum oxide.
 5. The composition as recited in claim 1 wherein the alkali metal azide is sodium azide.
 6. The composition as recited in claim 1 wherein the alkali metal azide is lithium azide.
 7. The composition as recited in claim 1 wherein the alkali metal azide is potassium azide.
 8. A gas generating composition which generates non-toxic, non-corrosive, odorless decomposition products consisting essentially of a. 50.16 percent NaN3 b. 40.75 percent Anhydrous CrCl3, and c. 9.09 percent Al2O3.
 9. A gas generating composition which generates non-toxic, non-corrosive, odorless decomposition products consisting essentially of a. 43.47 percent LiN3 b. 46.53 percent Anhydrous CrCl3, and c. 10 percent Al2O3.
 10. The method of making a gas generating composition containing an alkali metal azide, anhydrous chromic chloride, and aluminum oxide which comprises the steps of: a. screening the alkali metal azide to obtain granules having a particle size of about -70 mesh; b. grinding an anhydrous chromic chloride to an average particle diameter of from 1 to 3 microns; c. blending an alkali metal azide, chromic chloride, and aluminum oxide to produce an intimate mixture of solids; d. pressing the intimate solids mixture to produce pellets of gas generating composition; e. grinding the pellets to produce granules of gas generating composition; and f. screening the granules of gas generating composition to recover a fraction having a particle size of from -6 to +10 mesh.
 11. The method as recited in claim 10 wherein the granules having a particle size of -20 mesh are repressed into pellets having a diameter of about 1/4 inch and a thickness of 0.05 inch. 